Project Summary Cisplatin is a commonly used chemotherapeutic agent with dose-limiting nephrotoxicity. 30% of patients who receive cisplatin develop acute kidney injury (AKI), or a rapid decrease in kidney function. Development of AKI increases the risk of chronic kidney disease (CKD) and mortality. Even patients that do not develop AKI by clinical standards are still at risk for long term declines in renal function and CKD development. There are currently no therapies approved to prevent or treat cisplatin-induced kidney injury (CDDP-KI). In the past, research on CDDP-KI utilized a single, high dose model of injury. This model is lethal to mice within 3-4 days and does not allow for study of long-term renal outcomes. We have developed a more clinically relevant repeated low dose cisplatin (RLDC) model of CDDP-KI. In this model, mice receive 4 weekly low doses of cisplatin and can survive more than 6 months after treatment [1]. This RLDC model has been shown to induce renal fibrosis and progressive declines in renal function indicative of CKD development [1, 2]. Other models of kidney fibrosis have demonstrated that macrophages can play a pro-fibrogenic role by differentiating into myofibroblasts, the main effector of fibrotic development. Our preliminary studies show that the RLDC model causes accumulation of macrophages and myofibroblasts that persists up to 6 months after treatment. This is accompanied by a sustained increase in transforming growth factor beta (TGF?), which is a mediator of macrophage to myofibroblast transition. Lastly, we have identified a population of F4/80+ ?SMA+ CD206+ cells that appear after the fourth dose of cisplatin, indicative of this transition state. This research proposal will examine the relationship between macrophage response and susceptibility to CDDP-KI using our RLDC model of cisplatin-induced injury. We hypothesize that the repeated low dose cisplatin model promotes fibrosis and CKD development through stimulating chronic macrophage activity and macrophage to myofibroblast transition in the kidney. This hypothesis will be tested with the following aims. Aim 1: Characterize immune response and macrophage to myofibroblast transition during repeated low dose cisplatin. In this aim, we will use flow cytometry to analyze the immune cell response to cisplatin induced injury in the kidney. We will also isolate renal macrophages following cisplatin treatment and perform RNAseq to evaluate development of myofibroblast characteristics. Lastly, we will utilize bone marrow chimera models to determine if bone marrow derived immune cells are infiltrating the kidney following cisplatin treatment. Aim 2: Determine the role of macrophages in repeated low dose cisplatin induced fibrosis and chronic kidney disease. In this aim, we will determine how global depletion of macrophages and inhibition of chemokine (C-C motif) receptor 2 (CCR2) monocyte trafficking affects renal function and development of fibrosis in our RLDC model. Completion of these aims will identify novel targets to prevent the AKI to CKD transition associated with CDDP-KI.